Re: own bags? My experience...
The whole weighing the items scenario is utterly pointless. If someone is going to nick something they'll already have hidden it in another bag or in their coat, they're not going to scan it then conceal it or just stick it in the bagging area unscanned so whats the fucking point??
What really gets me with them (enough that I don't shop at Pak'n'Save any more, and never will enter another of their stores - yes these things DO matter!) is when I have scanned an item and put in down in the "bagging area", then my mate picks it up and puts it into a bag. Or I pick a full bag up to move it so I can get another bag. And the bloody machine basically accuses me of stealing, calls for assistance etc etc etc. If I wanted to steal the items I WOULDN'T HAVE SCANNED THE BLOODY THINGS IN THE FIRST PLACE!
(Thankfully not all companies are like this, and I usually prefer "the human touch" anyway, only using the automated systems when I have to or when the checkouts are heavily loaded or seriously lacking in eye candy...)